Effects of Nitrogen Addition on Nematode Communities in Northeastern Chinese Forests

Nitrogen deposition has a significant impact on biodiversity and ecosystem functions. However, various mechanisms by which nitrogen deposition affects soil nematode communities in nitrogen-limited temperate forests remain unclear. We conducted long-term nitrogen deposition simulation experiments (including two treatments, control and 50 kg N ha⁻1 yr⁻1) in the Lesser Khingan Range, Greater Khingan Range, and Changbai Mountain, applying nitrogen fertilizer solutions to investigate the effects of long-term nitrogen addition on soil nematode communities in northeastern Chinese forests. Nitrogen addition significantly decreased the total abundance of soil nematodes in the Lesser Khingan Range, Greater Khingan Range, and Changbai Mountain by 20%, 23%, and 18%, respectively. Furthermore, nitrogen addition reduced the α-diversity of soil nematodes and altered the β-diversity indices. The nematode channel ratio increased significantly, while the relative abundance of bacterivores, such as Euteratocephalus, also rose. In contrast, the structure index of the soil nematode community decreased, whereas the basal index increased. These results suggest that nitrogen addition simplifies the soil nematode community structure, which may be an important factor contributing to the decline in ecosystem function. Therefore, we selected soil nematodes as the research subject to provide a scientific basis for the effective protection, sustainable management, and resource utilization of major forest ecosystems in northeastern China under the context of nitrogen deposition.